1. Field of the Invention
The present invention relates to an apparatus for investigating particles in a fluid. It is particularly, but not exclusively, concerned with an apparatus for investigating urinary sediments in urine, or blood cells in blood. The present invention also relates to a method of operation of such an apparatus.
2. Summary of the Prior Art
The standard way of analyzing urinary sediments is by shape and size. Samples of urine are separated into liquid and sediment, using a centrifugal separation arrangement. Then, the sediment is dyed and the dyed sediment is studied by means of a microscope. It is important to know the concentration of sediment in the urine, and therefore the rate of centrifugal separation, and the quantities of samples investigated are constant. Originally, such investigation was carried out entirely manually, but attempts have been made to automate the analysis.
In U.S. Pat. No. 4,338,024 (corresponding to JP-A-57-500995), it was proposed that a flow of the fluid containing the particles was guided through a suitable guide means, such as a flow cell, and images were then generated of the flow at a particular point in that flow path. A CCD camera was used as an image means to observe the particles, and an enlarged image could then be generated. The CCD camera was operated periodically, with a fixed time between operations. Furthermore, U.S. Pat. No. 4,338,024 mentioned the use of the images to derive a particle concentration (density) measurement.
Furthermore, in JP-A-63-94156, there was separate detection and imaging of the particles. The particles were detected at a first point in the flow path by a particle detector, and the image means was triggered only when a particle was detected. The image means was located downstream of the particle detector, so that a suitable delay imposed on the triggering could enable a particle detected by the particle detector to be observed by the image means.